In the US that’s true (according to Wikipedia), but in a lot of places around the world, landing strips on the highway used to be (or still are) a thing. https://en.m.wikipedia.org/wiki/Highway_strip
yeah, i would think that, generally (maybe even universally), the interstate roads in the us are neither wide nor thick enough to support aircraft. i didn’t realise that there are countries that actually did this though; that’s pretty neat.